Out of the box, you should be able to use Mini and Javascript - the documentation should appear on the website within 24 hours (and we will keep updating it - sorry for inconvenience).

If you find bugs, best is to report them creating issues (1 issue per bug - don’t be afraid creating many issues) https://github.com/stencila/desktop/issues (it’s possible that some bugs are already reported there but maybe you can add a comment if you see them too).
You can also use this form https://goo.gl/forms/JJGvfGridRteyH9B3 for feedback. Including suggestions for new features and improvements. What would you like to see in Stencila?